Bacterial Communities Associated with the Pine Wilt Disease Insect VectorMonochamus alternatus(Coleoptera: Cerambycidae) during the Larvae and Pupae Stages

Monochamus alternatusis an important insect pest in pine forests of southern China and the dispersing vector of the pine wood nematode,Bursaphelenchus xylophilus, which leads to pine wilt disease (PWD). Microbiome ofM. alternatusmay contribute to survival of larvae in the host pine trees. In order to investigate the intestinal bacterial structure ofM. alternatusduring the larvae and pupae stages in host trees, and infer the function of symbiotic bacteria, we used 16S rRNA gene Illumina sequencing to obtain and compare the bacterial community composition in the foregut, midgut, and hindgut of larvae, pupal intestines, larval galleries, and pupal chambers ofM. alternatus. The diversity of the bacterial community in larval intestines and pupal intestines were similar, as well as was significantly greater in larval galleries and pupal chambers. Although there were differences in bacterial compositions in different samples, similar components were also found. Proteobacteria and Firmicutes were the two most dominant phyla in all samples, and generaEnterobacter,Raoultella,Serratia,Lactococcus, andPseudomonaswere dominant in both the intestinal samples and plant tissue samples.Enterobacterwas the most abundant genus in larval intestines, andSerratiawas dominant in pupal intestine. The functions of these dominant and specific bacteria were also predicted through metagenomic analyses. These bacteria may helpM. alternatusdegrade cellulose and pinene. The specific role of symbiotic bacteria in the infection cycle of PWD also warrants further study in the future.